Not so simple: Gulping bugs with the nuclear option

One bacterium breaks two rules: it’s got something like a nucleus, and it swallows its food

The defining characteristic of simple cells, or prokaryotes, is supposed to be the fact that their DNA floats freely in the cell rather than being enclosed in a nucleus. Indeed, the term “prokaryote” means “before nucleus”.

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Then, in 1991, John Fuerst and Richard Webb of the University of Queensland in Brisbane, Australia, noticed something strange about Gemmata obscuriglobus, a bacterium first described in 1984. It seemed to have “packaged” DNA. Images taken with an electron microscope confirmed that not only was its DNA separate from the rest of the cell, it was enclosed by a double membrane – just like the membrane envelope surrounding the nucleus of complex cells.

So is G. obscuriglobus, along with other members of the Planctomycete group to which it belongs, really a prokaryote? Its nucleus, such as it is, is not nearly as sophisticated as that of complex cells, and genetically it is very much like other bacteria. So many biologists were inclined to treat its “nucleus” as a curiosity unrelated to that of complex cells – until this bacterium was found to have another extraordinary trait…

They can swallow

Complex cells like amoebae (pictured right) and white blood cells can “swallow” large particles by engulfing them and pinching off the “bubble” containing the particle, a process called endocytosis. Bacteria were only thought to be able to take in particles via …